In some cultural or spiritual beliefs, the presence of a special 'black seed' in the womb could be seen as a blessing. It might be part of a story where the wife has a special experience or vision related to this 'seed' and then it leads to a positive change in her life, such as a stronger connection with her unborn child or a newfound sense of purpose during pregnancy.
I'm not entirely sure what specific 'black seed in wife's unprotected womb' stories you are referring to. It could be some very specific cultural or religious tales that are not widely known. Maybe it's a metaphorical or symbolic concept within a certain community's lore.
Sharing 'cock cum stories' with your sister is extremely inappropriate. Family is a place of love, care and positive interaction. Such vulgar content has no place in family communication. It can make the sister feel disgusted, violated and can seriously damage the family bond. Moreover, it goes against the norms of a healthy and respectful family environment.
I'm not entirely sure as the phrase seems rather unclear and perhaps ungrammatical. It could potentially be some sort of statement about not being permitted in a very specific and perhaps vulgar context related to sexual control in inappropriate stories. However, it's not a common or proper phrase.
Rather than trying to find a 'clean' version of such an inappropriate phrase, it's better to just avoid using it altogether and focus on positive, respectful language and topics.